This invention relates to a diagnostic nuclear medical apparatus and, more particularly, to image processing for an apparatus using a digital scintillation camera.
Diagnostic nuclear medical apparatuses are utilized for the diagnosis of subjects (human patients) through detection of the distribution of gamma rays emitted from the subject dosed with radioisotopes (hereinafter referred to as RI). In a prior art gamma camera system, gamma rays emitted from the interior of the subject are detected by a gamma camera having a two-dimensional detection surface, and position signals indicative of positions at which gamma rays are detected are fed to a gamma imager. The gamma imager exposes an X-ray film with luminescent spots according to the detected distribution of the gamma rays to obtain a scintigram (an RI distribution image).
Recently, digital scintillation camera systems have been applied in practice to obtain a scintigram of subject. Diagnostic data (position data) obtained from a scintillation camera is converted by an analog-to-digital converter into digital data for storage in an image memory. In the memory, the number of times (i.e., counts) gamma rays are detected at each position (i.e., each pixel on the detection surface of the camera) is stored as data. Data is read out from the image memory in the order of addresses corresponding to picture elements on the camera detection surface for conversion by a digital-to-analog converter into analog information. The analog information is further converted into a video signal for displaying the RI detection times at graduated levels of brightness. The video signal is fed to a video imager to display a luminescent spot image on a TV monitor. The luminescent spot image is imaged (photographed) by a multi-format camera on an X-ray film. A portion of the subject where the RI detection count is large is displayed with high brightness on the TV monitor. A portion where the RI detection count is high, on the other hand, is imaged black on the X-ray film, i.e., it is photographed at a high photographic density. The relation between the video signal amplitude level and X-ray film photographic density is peculiar to a film photographing system (including a TV monitor, X-ray film, developing unit and liquid developer).
With such a diagnostic apparatus, in many cases, a contrast between a region-of-interest and other regions imaged on the X-ray film provides important information for the diagnosis. Therefore, it is desired to photograph the region-of-interest at an optimum density. Otherwise, erroneous diagnosis is liable to result.
In the digital scintillation camera system, the video signal gray scale (GRAY) has 256 levels from 0 to 255, for instance. The display count scale (WINDOW), i.e., the gamma ray detection times, has 4,096 count levels of 0 to 4095, for instance. The display gray scale level is linearly proportional to the video signal amplitude level (in volts). The GRAY scale and WINDOW scale may be arbitrarily set through a keyboard of a computer system by an operator. For example, 10 to 50 counts may be made to correspond to a gray scale of 20 to 100. For this reason, it is possible to freely determine the relation between the WINDOW level and X-ray film photographic density. Once this relation is determined, the relation the WINDOW level and GRAY scale can be determined.
The quality such as density and contrast of image on the X-ray film is influenced by the type of an X-ray film used, an elapsed period after the manufacture of the film, and developing conditions (developing unit, liquid developer, etc.). The upper and lower limits of gamma-ray detection counts depend on the kind of an organ to be diagnosed and the kind of a radioactive medicine used. Therefore, the image quality is also influenced by these conditions. Therefore, in order to obtain the optimum image quality for the diagnosis, it is necessary to determine optimum image processing conditions for each diagnosis. This is, however, time-consuming.
A copending U.S. patent application No. 793,767 entitled "Digital Scintillation Camera System" filed on Nov. 1, 1985 and assigned to the same assignee as this application discloses an improved digital scintillation camera system.